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Pre-Treatment Plants

PRE-TREATMENT PLANTS

Flat spray nozzles produce impact sprays, with narrow angles.

They are very efficient for use in the "Pre-Treatment" process that many products go through before paint dipping applcations. "Pre-treatment" ensures that product is clean and often applies protective coatings such as phosphate, chromate or a paint primer.

- A large number of different products are cleaned this way

For exampke, car bodies and car panels, washing machine, refrigeration and dishwasher csing all pass through a similar pre-paint finishing proces

The process almost always zoned with the first zone being a de-greasing or chemical detergent operation, or "knock-off zone"

In some plants, for example, the car industry, the first de-greasing operation is split into two zones

The first cleaning zone is often called the "knock-off zone"

The flat spray nozzle with high pressure and high volume means that large pieces of waste material can be removed easily as the product passes through the cleaning zone.

A second, de-greasing znone is sometimes used to remove smaller pieces of waste from the product

More zones are usually used to wash and phosphate or chromate dip the product before a primer is applied ready for painting

The product, whether a car body or smaller item such as  washing machine casing, is moved through the cleaning system using a moving hanger as shown in the diagram. Quick couplers are used to attach the manifolds to the supple pipe so that they can be easily removed for cleaning or replacement when the car body design changes. Removable end caps allow the manifolds to be cleaned more easily.

Application Sheet:

The flat spray nozzles used in this application are as follows:

The spray angle depends on the distance from the nozzle to the product but typically 50° or 65° are used on AC and 35° on TJ nozzles

- In a car body plant, for example, the AC nozzles are used for most requirements

The TJ nozzles are used to spray the underside of the car body and have a reach of over 1 metre

The use of Ball Swivel, spray clip eyelets or AP Ball Jets allows the spray direction to be altered to fit different product needs

Nozzle Material:

Most installations use stainless steel nozzles, however there is a general move towards the use of plastic materials in modern plants, because of cost and maintenance

This is mainly because of the esae of nozzle cleaning and maintenance given by the plastic design

The most common material used for plastic nozzles and threaded balls is polypropylene with pipework being fabracated from cVPC mateiral

All plastic nozzle materials (AP Ball Jets) used in paint plants must be specified silicone fre

Silicone is used on the mouldingof rubber components and if it is not removed it will contaminate the metal surfaces being cleaned

If a metal surface becomes contaminated with silicone, paint will not stick to it.

Maintenance Period:

When the nozzle fitted is tainless steel, it will not be changed very frequently

Most manufactureres are trying to convince end users that plastic is a better materials

- it is more suitable and more cost effective

Moulded plastic itesm are such less expensive ad can threefore be changed more often

The recommended change period is between three and six months

In the phosphate cleaning zone it is much more chemically aggressive and there is a need to change nozzles as frequently as every month

Worn nozzles do not currently spray the product.

eductors

Eductors are used in dip tanks to circulate the liquid

The eductors are used to cause a flow of the liquid contained in the dip tank - this effect is called agitation, and is necessary to keep solids in suspension. Agitation is required to make sure that the liquid is well circulated and completely covers the product

Tanks are emptied 1-2 times a year and some tanks have acid wash applied

The dip tanks used in the car industry are usually between two and three cars in length.

Each tank will have up to thirty eductors fitter depending on tank size. The eductors are fitted into the tank on a ladder pattern as shown in the diagram.

The most common size of eductor used in the car industry is 3/4 inch BB300

This nozzle gives a liquid turnover of 3:1. This means that the volume of liquid drawn in is about 3 times the volume of e liquid pumped through the nozzle orifice.